Differential quadrature phase shift keying system, method, and device

Abstract

A differential quadrature phase shift keying (DQPSK) system, method, and device are disclosed. The DQPSK system includes: a transmitter, configured to: pre-code an input first signal and second signal, and generate an in-phase signal and a quadrature signal; modulate the in-phase signal to generate a first differential phase shift keying (DPSK) signal, and modulate the quadrature signal to generate a second DPSK signal; perform a 90 degree phase shift on the first DPSK signal or the second DPSK signal, and interfere with the other DPSK signal to obtain a DQPSK signal; and send the DQPSK signal to a receiver; the receiver, configured to: demodulate the DQPSK signal sent from the transmitter in detuned filter mode, and restore the first signal and the second signal through optical/electrical (o/E) conversion. With the present invention, the accurate control on the phase difference between two arms of an Asymmetric Mach-Zehnder Interferometer (AMZI) is avoided, thus facilitating the signal control and adjustment, and greatly lowering the system cost.

1 . A differential quadrature phase shift keying (DQPSK) system, comprising a transmitter, wherein the transmitter comprises:
 a pre-coder, configured to pre-code a first signal and a second signal according a predetermined encoding rule, and generate an in-phase signal and a quadrature signal;   a first modulator, configured to modulate the in-phase signal to generate a first differential phase shift keying (DPSK) signal;   a second modulator, configured to modulate the quadrature signal to generate a second DPSK signal; and   an interferometer, configured to: perform a 90 degree phase shift on the first DPSK signal or the second DPSK signal, interfere with and overlap with the other DPSK signal to obtain a DQPSK signal, and send the DQPSK signal to a receiver.   
     
     
         2 . The system of  claim 1 , further comprising the receiver, wherein:
 the receiver comprises:   a splitter, configured to split the DQPSK signal sent from the transmitter into two signals, and output the two signals; and   a demodulator, configured to demodulate the two DQPSK signals output by the splitter.   
     
     
         3 . The system of  claim 1 , wherein the modulators are Mach-Zehnder modulators (MZMs);
 the first MZM is configured to obtain the first DPSK signal through modulation and driving by using the in-phase signal;   the second MZM is configured to obtain the second DPSK signal through modulation and driving by using the quadrature signal; and   the interferometer is configured to: perform the 90 degree phase shift on the first DPSK signal or the second DPSK signal, interfere with the other DPSK signal to obtain the DQPSK signal, and send the DQPSK signal to the receiver.   
     
     
         4 . The system of  claim 2 , wherein the demodulator comprises a first detuned filter and a second detuned filter;
 the first detuned filter is configured to demodulate one DQPSK signal output by the splitter in detuned filter mode, and output the demodulated DQPSK signal; and   the second detuned filter is configured to demodulate the other DQPSK signal output by the splitter in detuned filter mode, and output the demodulated DQPSK signal.   
     
     
         5 . The system of  claim 1 , wherein the receiver comprises a detuned filter and a splitter;
 the detuned filter is configured to demodulate the DQPSK signal sent from the transmitter in detuned filter mode, and output the demodulated DQPSK signal to the splitter; and   the splitter is configured to split the signal demodulated by the detuned filter into two demodulated signals, and output the two signals.   
     
     
         6 . The system of  claim 1 , wherein the predetermined encoding rule is:
     I   k   =uvI     k -1   +ūvQ   k-1   +u  v Q     k -1   +ū  v I   k-1        or       Q   k   =uvQ     k -1   +ūvI     k -1   +u  v I   k-1   +ū  v Q   k-1          I   k   =  v I   k-1   Q     k -1   +uI     k -1   Q     k -1   +ūI   k-1   Q   k-1   +vI     k -1   Q   k-1          Q   k   =ūI     k -1   Q   k-1   +vI     k -1   Q     k -1   +uI   k-1   Q     k -1   +  v I   k-1   Q   k-1      wherein: u refers to the first signal, and v refers to the second signal; and   I refers to the pre-coded in-phase signal, and Q refers to the pre-coded quadrature signal.   
     
     
         7 . The system of  claim 2 , wherein the predetermined encoding rule is:
     I   k   =uvI     k -1   +ūvQ   k-1   +u  v Q     k -1   +ū  v Q   k-1        or       Q   k   =uvQ     k -1   +ūvI     k -1   +u  v I   k-1   +ū  v Q   k-1          I   k   =  v I   k-1   Q     k -1   +uI     k -1   Q     k -1   +ūI   k-1   Q   k-1   +vI     k -1   Q   k-1          Q   k   =ūI   k-1   Q     k -1   +uI     k -1   Q     k -1   +ūI   k-1   Q   k-1   +vI     k -1   Q   k-1      wherein: u refers to the first signal, and v refers to the second signal; and   I refers to the pre-coded in-phase signal, and Q refers to the pre-coded quadrature signal.   
     
     
         8 . The system of  claim 3 , wherein the predetermined encoding rule is:
     I   k   =uvI     k -1   +ūvQ   k-1   +u  v Q     k -1   +ū  v I   k-1        or       Q   k   =uvQ     k -1   +ūvI     k -1   +u  v I   k-1   +ū  v Q   k-1          I   k   =  v I   k-1   Q     k -1   +uI     k -1   Q     k -1   +ūI   k-1   Q   k-1   +vI     k -1   Q   k-1          Q   k   =ūI     k -1   Q   k-1   +vI     k -1   Q     k -1   +uI   k-1   Q     k -1   +  v I   k-1   Q   k-1      wherein: u refers to the first signal, and v refers to the second signal; and   I refers to the pre-coded in-phase signal, and Q refers to the pre-coded quadrature signal.   
     
     
         9 . The system of  claim 4 , wherein the predetermined encoding rule is:
     I   k   =uvI     k -1   +ūvQ   k-1   +u  v Q   k-1   +ū  v I   k-1        or       Q   k   =uvQ     k -1   +ūvI     k -1   +u  v I   k-1   +ū  v Q   k-1          I   k   =  v I   k-1   Q     k -1   +uI     k -1   Q     k -1   +ūI   k-1   Q   k-1   +vI   k-1   Q   k-1          Q   k   =ūI     k -1   Q   k-1   +vI     k -1   Q     k -1   +uI   k-1   Q     k -1   +  v I   k-1   Q   k-1      wherein: u refers to the first signal, and v refers to the second signal; and   I refers to the pre-coded in-phase signal, and Q refers to the pre-coded quadrature signal.   
     
     
         10 . The system of  claim 5 , wherein the predetermined encoding rule is:
     I   k   =uvI     k -1   +ūvQ   k-1   +u  v Q   k-1   +ū  v I   k-1        or       Q   k   =uvQ     k -1   +ūvI     k -1   +u  v I   k-1   +ū  v Q   k-1          I   k   =  v I   k-1   Q     k -1   +uI     k -1   Q     k -1   +ūI   k-1   Q   k-1   +vI     k -1   Q   k-1          Q   k   =ūI     k -1   Q   k-1   +vI     k -1   Q     k -1   +uI   k-1   Q     k -1   +  v I   k-1   Q   k-1      wherein: u refers to the first signal, and v refers to the second signal; and   I refers to the pre-coded in-phase signal, and Q refers to the pre-coded quadrature signal.   
     
     
         11 . A differential quadrature phase shift keying (DQPSK) system, comprising:
 a transmitter, configured to: pre-code N first signals and N second signals according to a predetermined encoding rule to generate N in-phase signals and N quadrature signals; modulate the N in-phase signals to generate N first differential phase shift keying (DPSK) signals, and modulate the N quadrature signals to generate N second DPSK signals; perform a 90 degree phase shift on the N first DPSK signals or the N second signals, and interfere with and overlap with the other N DPSK signals to obtain N DQPSK signals; multiplex the N DQPSK signals into an N-channel DQPSK signal; and send the N-channel DQPSK signal to a receiver; and   the receiver, configured to: demultiplex the N-channel DQPSK signal sent from the transmitter into N DQPSK signals in detuned filter mode to restore the N first signals and the N second signals, wherein N is an integer greater than 1.   
     
     
         12 . A method for processing signals, comprising:
 by a transmitter, pre-coding an input first signal and second signal, and generating an in-phase signal and a quadrature signal; modulating the in-phase signal to generate a first differential phase shift keying (DPSK) signal, and modulating the quadrature signal to generate a second DPSK signal; performing a 90 degree phase shift on the first DPSK signal or the second DPSK signal, and interfering with the other DPSK signal to obtain a differential quadrature phase shift keying (DQPSK) signal.   
     
     
         13 . The method of  claim 12 , wherein an encoding rule on which the pre-coding is based is:
     I   k   =uvI     k -1   +ūvQ   k-1   +u  v Q     k -1   +ū  v I   k-1        or       Q   k   =uvQ     k -1   +ūvI     k -1   +u  v I   k-1   +ū  v Q   k-1          I   k   =  v I   k-1   Q     k -1   +uI     k -1   Q     k -1   +ūI   k-1   Q   k-1   +vI     k -1   Q   k-1          Q   k   =ūI     k -1   Q   k-1   +vI     k -1   Q     k -1   +uI   k-1   Q     k -1   +  v I   k-1   Q   k-1      wherein: u refers to the first signal, and v refers to the second signal; and   I refers to the pre-coded in-phase signal, and Q refers to the pre-coded quadrature signal.   
     
     
         14 . The method of  claim 12 , wherein an encoding rule on which the pre-coding is based is:
     I   k   =ū  v I   k-1   +ūvQ     k -1   +uvI     k -1   +u  v Q   k-1        or       Q   k   =ū  v Q   k-1   +u  v I     k -1   +ūvI   k-1   +uvQ     k -1          I   k   =ūI   k-1   Q     k -1   +vI     k -1   Q     k -1   +uI     k -1   Q   k-1   +  v I   k-1   Q   k-1          Q   k   =  v I     k -1   Q   k-1   +uI     k -1   Q     k -1   +ūI   k-1   Q   k-1   +vI   k-1   Q     k -1      wherein: u refers to the first signal, and v refers to the second signal; and   I refers to the pre-coded in-phase signal, and Q refers to the pre-coded quadrature signal.   
     
     
         15 . The method of  claim 12 , further comprising: sending, by the transmitter, the DQPSK signal; and
 by the receiver, demodulating the received DQPSK signal in detuned filter mode; and restoring the first signal and the N second signals from the demodulated signal through optical/electrical (O/E) conversion.   
     
     
         16 . A method for processing signals, comprising:
 by a transmitter, pre-coding input N first signals and N second signals, and generating N in-phase signals and N quadrature signals;   modulating the N in-phase signals to generate N first non-return-to-zero differential phase shift keying (NRZ-DPSK) signals, and modulating the N quadrature signals to generate N second DPSK signals; and   performing a 90 degree phase shift on the N DPSK signals or the N second DPSK signals, interfering with the other N DPSK signals to obtain N DQPSK signals, and multiplexing the N DQPSK signals into an N-channel DQPSK signal, wherein N is an integer greater than 1.   
     
     
         17 . The method of  claim 16 , further comprising: sending, by the transmitter, the N-channel DQPSK signal; and
 by the receiver, demultiplexing the received N-channel DQPSK signal into N DQPSK signals, demodulating the N DQPSK signals in detuned filter mode, and restoring the N first signals and the N second signals through optical/electrical (O/E) conversion.